I get that images - even once deleted - are stored in some form on the device, but surely the mobile service provider can dig out the text thread, and the context in which you received the image (unsolicited) should show your innocence in the matter?
*Aren't all text messages retrievable from the service provider? Admittedly it will take a fair bit of digging and requests.
*Maybe could be the result of watching too many CSI type programs. . . .